System and method for forming perforations in a barrel section

ABSTRACT

A drilling system may include a plurality of robotic drilling units. Each one of the robotic drilling units may include a drill end effector positioned inside a barrel section. The barrel section may be configured as a composite sandwich structure having an inner face sheet. The robotic drilling units maybe operable in synchronized movement with one another to drill a plurality of perforations into the inner face sheet using the drill end effectors in a manner providing a predetermined percent-open-area of the inner face sheet.

FIELD

The present disclosure relates generally to production of acoustictreatment of structures and, more particularly, to the forming ofacoustic perforations in an engine inlet barrel section.

BACKGROUND

Commercial airliners are required to meet certain noise standards suchas during takeoff and landing. A large portion of the noise produced bya commercial airliner during takeoff and landing is generated by gasturbine engines commonly used on airliners. Known methods for reducingthe noise level of a gas turbine engine include acoustically treatingthe engine inlet of the engine nacelle. In this regard, the inner barrelsection of a gas turbine engine inlet may be provided with a pluralityof relatively small perforations formed in the walls of the inner barrelsection. The perforations absorb some of the noise that is generated byfan blades rotating at high speed at the engine inlet, and therebyreduce the overall noise output of the gas turbine engine.

Conventional methods for forming perforations in acoustic structuressuch as the barrel section include forming the inner wall of the barrelsection as a separate component, followed by forming the perforations inthe inner wall. The inner wall may then be assembled with othercomponents that make up the barrel section, which is then assembled withthe nacelle of the gas turbine engine. Unfortunately, such conventionalmethods for forming acoustic structures include operations that mayresult in the blockage of some of the perforations after theperforations have been formed.

Conventional methods for forming acoustic structures may also result inmissing perforations. Such blocked perforations or missing perforationsmay reduce the percent-open-area (POA) of the inner wall (e.g., thetotal area of the perforations as a percentage of the surface area ofthe inner wall) which is a characteristic of acoustic structures formeasuring their overall effectiveness in absorbing or attenuating noise.Furthermore, conventional methods of forming perforations in acousticstructures are time-consuming processes that add to the productionschedule and cost.

As can be seen, there exists a need in the art for a system and methodfor forming perforations in an acoustic structure which minimizes oreliminates the occurrence of blocked or missing perforations, and whichmay be performed in a timely and cost-effective manner.

SUMMARY

The above-noted needs associated with forming perforations in anacoustic structure such as an engine inlet are specifically addressedand alleviated by the present disclosure which provides a drillingsystem that may include a plurality of robotic drilling units. Each oneof the robotic drilling units may include a drill end effectorpositioned inside a barrel section of an engine inlet. The barrelsection may be configured as a composite sandwich structure having aninner face sheet. The robotic drilling units may be operable insynchronized movement with one another to drill a plurality ofperforations into the inner face sheet using the drill end effectors ina manner providing a predetermined percent-open-area of the inner facesheet.

Also disclosed is a method of fabricating an engine inlet. The methodmay include providing an engine inlet inner barrel section configured asa composite sandwich structure having an inner face sheet, a core, andan outer face sheet. The method may further include robotically drillinga plurality of perforations in the inner face sheet after final cure ofthe composite sandwich structure. The method may additionally includeforming the plurality of perforations in a quantity providing apredetermined percent-open-area of the inner face sheet.

In a further embodiment, disclosed is a method of fabricating an engineinlet including the step of providing an engine inlet inner barrelsection configured as a one-piece composite sandwich structure having aninner face sheet, an outer face sheet, and a honeycomb core. Thecomposite sandwich structure may be formed in a single stage curewherein the inner face sheet, the core, and the outer face sheet may beco-cured and/or co-bonded in a single operation. The method may includedrilling, using a plurality of robotic drilling units, a plurality ofperforations in the inner face sheet after final cure of the compositesandwich structure. The method may further include operating theplurality of robotic drilling units in synchronized movement with oneanother to simultaneously drill the plurality of perforations. Themethod may also include forming the plurality of perforations in aquantity providing a predetermined percent-open-area of the inner facesheet.

The features, functions and advantages that have been discussed can beachieved independently in various embodiments of the present disclosureor may be combined in yet other embodiments, further details of whichcan be seen with reference to the following description and drawingsbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the present disclosure will become moreapparent upon reference to the drawings wherein like numbers refer tolike parts throughout and wherein:

FIG. 1 is a perspective illustration of an aircraft;

FIG. 2 is a perspective illustration of a nacelle of a gas turbineengine of the aircraft of FIG. 1;

FIG. 3 is a perspective illustration of an inner barrel section of anengine inlet of the gas turbine engine of FIG. 2;

FIG. 4 is a cross-sectional illustration of a leading edge of the engineinlet of the gas turbine engine of FIG. 2;

FIG. 5 is a perspective illustration of an embodiment of a drillingsystem for forming perforations in a barrel section;

FIG. 6 is a perspective illustration of the drilling system with thebarrel section shown in phantom lines to illustrate a plurality ofrobotic drilling units of the drilling system;

FIG. 7 is a side view of the drilling system;

FIG. 8 is the top view of the drilling system;

FIG. 9 is a side view of one of the robotic drilling units forming ahole pattern along an inner face sheet of the inner barrel section;

FIG. 10 is a perspective illustration of a drill end effector forming aperforation in an inner face sheet of a composite sandwich structure ofthe inner barrel section;

FIG. 11 is a cross sectional illustration taken along line 11 of FIG. 10and illustrating a drill bit of the drill end effector drilling aperforation in the inner face sheet of the composite sandwich structure;

FIG. 12 is a block diagram of an embodiment of the drilling system;

FIG. 13 is an illustration of a flow chart including one or moreoperations that may be implemented in a method of fabricating an engineinlet;

FIG. 14 is a flow diagram of an aircraft manufacturing and servicemethodology; and

FIG. 15 is a block diagram of an aircraft.

DETAILED DESCRIPTION

Referring now to the drawings wherein the showings are for purposes ofillustrating various embodiments of the present disclosure, shown inFIG. 1 is a perspective illustration of an aircraft 100. The aircraft100 may include a fuselage 102 extending from a nose to an empennage104. The empennage 104 may include one or more tail surfaces fordirectional control of the aircraft 100. The aircraft 100 may include apair of wings 106 extending outwardly from the fuselage 102.

In FIG. 1, the aircraft 100 may include one or more propulsion unitswhich, in an embodiment, may be supported by the wings 106. Each one ofthe propulsion units may be configured as a gas turbine engine 108having a core engine (not shown) surrounded by a nacelle 110. Thenacelle 110 may include an engine inlet 114 and a fan cowl 118surrounding one or more fans (not shown) mounted on a forward end (notshown) of the core engine. The nacelle 110 may have an exhaust nozzle112 (e.g., a primary exhaust nozzle and a fan nozzle) at an aft end (notshown) of the gas turbine engine 108.

FIG. 2 illustrates an embodiment of a gas turbine engine 108 having anengine inlet 114. The engine inlet 114 may include a leading edge 116and an inner barrel section 120 located aft of the leading edge 116 ofthe engine inlet 114. The inner barrel section 120 may provide aboundary surface or wall for directing airflow (not shown) entering theengine inlet 114 and passing through the gas turbine engine 108. Theinner barrel section 120 may be located in relatively close proximity toone or more fans (not shown). In this regard, the inner barrel section120 may also be configured to serve as an acoustic structure having aplurality of perforations 136 (FIG. 9) in an inner face sheet 134 (FIG.10) of the inner barrel section 120 for absorbing noise generated by therotating fans and/or noise generated by the airflow entering the engineinlet 114 and passing through the gas turbine engine 108.

As described below, the total area of the perforations 136 in the innerface sheet 134 may be expressed as percent-open-area 144 (FIG. 9) whichrepresents the total area of the perforations 136 as a percentage of thesurface area of the inner face sheet 134. The percent-open-area 144 maybe a characteristic for measuring the overall effectiveness oracoustic-attenuating capability of the inner barrel section 120. Duringthe design and/or development of the aircraft 100, a specific, apredetermined percent-open-area 144 (FIG. 9) may be selected for theinner barrel section 120 to meet acoustic performance requirements ofthe engine inlet 114.

FIG. 3 is a perspective illustration of an embodiment of an inner barrelsection 120 of an engine inlet 114. In the embodiment shown, the barrelsection 120 may have a diameter (not shown) of up to 5-8 feet or larger,and a length (not shown) extending from an aft edge 126 to a forwardedge 124 of up to 2-3 feet or longer. However, the barrel section 120may be provided in any size, shape, and configuration, withoutlimitation. The inner barrel section 120 may be formed as a compositesandwich structure 122 having an inner face sheet 134 and an outer facesheet 132 separated by a core 128. The inner face sheet 134 and/or theouter face sheet 132 may be formed of composite material includingfiber-reinforced polymeric matrix material such as graphite-epoxy,fiberglass-epoxy, or other composite material. Alternatively, the innerface sheet 134 and/or the outer face sheet 132 may be formed of metallicmaterial such as titanium, steel, or other metallic materials orcombinations of materials. The core 128 may comprise honeycomb corehaving a plurality of cells 130 oriented generally transverse to theinner face sheet 134 and outer face sheet 132. The core 128 may beformed of metallic material and/or non-metallic material and may includealuminum, titanium, aramid, fiberglass, or other core materials.

In FIG. 3, in an embodiment, the engine inlet 114 may comprise aone-piece engine inlet 114 inner barrel section 120. The inner barrelsection 120 may be fabricated from raw materials (not shown) andassembled and cured in one or more stages. For example, the inner facesheet 134 and the outer face sheet 132 may be separately formed bylaying up dry fiber fabric (not shown) or resin-impregnated ply material(i.e., pre-preg) on separate layup mandrels (not shown) and separatelycured, followed by bonding the inner face sheet 134 and the outer facesheet 132 to the core 128. Alternatively, the inner barrel section 120may be fabricated in a single-stage cure process wherein the inner facesheet 134 may be laid up on a layup mandrel (not shown), after which thecore 128 may be laid up over the inner face sheet 134, followed bylaying up the outer face sheet 132 over the core 128. The layup assembly(not shown) may be cured in a single stage, after which the drillingsystem 200 (FIG. 5) disclosed herein may be implemented for formingperforations 136 (FIG. 9) in the inner face sheet 134.

In an embodiment described in greater detail below, the drilling system200 (FIG. 5) disclosed herein may be implemented for forming a pluralityof perforations 136 (FIG. 9) in the inner face sheet 134 (FIG. 9) of theassembled barrel section 120. For example, the drilling system 200 (FIG.5) disclosed herein may include a plurality of robotic drilling units208 (FIG. 8) positioned inside the barrel section 120 for roboticallydrilling a plurality of the perforations 136 in the inner face sheet 134after final cure of the composite sandwich structure 122 engine inletinner barrel section 120. The perforations 136 (FIG. 9) may be formed ina size and quantity to provide a predetermined percent-open-area 144 forthe inner barrel section 120 to allow the inner barrel section 120 tomeet acoustic performance requirements of the engine inlet 114.

In FIG. 3, the inner barrel section 120 may comprise a unitary structurehaving closed shape with a generally cylindrical configuration. However,in an embodiment, the inner barrel section 120 may be formed as multiplesegments (not shown) assembled together to form a closed shape. Theinner barrel section 120 may be provided in a contoured cross-sectionalshape (not shown) to promote airflow (not shown) through the gas turbineengine 108. In this regard, when viewed along a circumferentialdirection, the inner barrel section 120 may have a cross section thatmay be complexly curved and may be formed complementary to the shape ofthe engine inlet 114 leading edge 116 at a forward edge 124 of the innerbarrel section 120, and complementary to the shape of the interiornacelle surfaces (not shown) aft of the inner barrel section 120.However, the inner barrel section 120 may be provided in any shapeincluding a simple cylindrical shape and/or a conical shape.

FIG. 4 is a cross-sectional illustration of the leading edge 116 of theengine inlet 114 showing the composite sandwich construction includingthe circumferential inner face sheet 134, the circumferential outer facesheet 132, and the core 128 separating the inner face sheet 134 andouter face sheet 132 of the barrel section 120. The forward edge 124 ofthe inner barrel section 120 may be coupled to or may interface with theengine inlet 114 leading edge 116. The aft edge 126 of the inner barrelsection 120 may be coupled to or may interface with the nacelle interior(not shown). In the embodiment shown, the inner face sheet 134, the core128, and the outer face sheet 132 have a complexly-curved crosssectional shape to promote efficient airflow through the nacelle 110.

FIG. 5 is an illustration of an embodiment of a drilling system 200 asmay be implemented for forming perforations 136 (FIG. 9) in a barrelsection 120 such as the inner barrel section 120 of an engine inlet 114of a gas turbine engine 108 (FIG. 3). However, the drilling system 200disclosed herein may be implemented for forming perforations 136 (FIG.9) in any type of barrel structure for any application, withoutlimitation. For example, the drilling system 200 may be implemented forforming perforations 136 (FIG. 9) in a barrel section of any one of avariety of different types of commercial, civilian, and militaryaircraft 100 (FIG. 1). Furthermore, the drilling system 200 may beimplemented for forming perforations 136 (FIG. 9) in the barrel section120 of a gas turbine engine 108 (FIG. 1) of rotorcraft, hovercraft, orin any other vehicular or non-vehicular application wherein apredetermined quantity of acoustic perforations 136 (FIG. 9) arerequired in a barrel section 120 for acoustic attenuating purposes.

In FIG. 5, the drilling system 200 is shown mounted within an interiorof a barrel section 120. The drilling system 200 may include roboticdrilling units 208 that advantageously allow for forming perforations136 (FIG. 9) in a barrel section 120 to provide the predeterminedpercent-open-area 144 (FIG. 9) of the inner face sheet 134 of the barrelsection 120. As indicated above, the predetermined percent-open-area 144may be determined during the design and/or development of the aircraft100 (FIG. 1) to meet acoustic performance requirements of the engineinlet 114. The drilling system 200 disclosed herein advantageouslyallows for consistently forming perforations 136 in the inner facesheets 134 of composite sandwich structure 122 barrel sections 120 toprovide a predetermined percent-open-area 144 (FIG. 9) in the inner facesheet 134. In this regard, the drilling system 200 advantageouslyovercomes the drawbacks associated with conventional methods for formingperforations (not shown) in conventional inner barrel sections (notshown) such as the above-mentioned drawbacks associated with blockedperforations (not shown) due to subsequent processing of a conventionalinner barrel section (not shown) in a conventional multi-stage formingprocess (not shown), and/or due to missing perforations (not shown)during conventional perforating (not shown) of the inner skin (notshown) of a conventional inner barrel section. Such blocked perforationsor missing perforations may reduce the predetermined percent-open-area144 of the inner skin of the conventional inner barrel section which mayreduce the acoustic performance of the engine inlet 114.

In FIG. 5, a plurality of robotic drilling units 208 (e.g., two roboticdrilling units 208, three robotic drilling units 208, etc.) may besupported on a system base 202. Each one of the robotic drilling units208 may include a drill end effector 234. In an embodiment, the systembase 202 may comprise a relatively rigid structure and may include atooling fixture, a shop floor, or a table configured to support theplurality of robotic drilling units 208. In addition, the system base202 may be configured to support the barrel section 120. However, thedrilling system 200 may be provided in an alternative embodiment whereinthe plurality of robotic drilling units 208 are supported by a structurethat is located separate from the barrel section 120. For example, theplurality of robotic drilling units 208 may be suspended over the innerbarrel section 120 such as by an overhead fixture (not shown) in amanner such that the drill end effectors 234 may be positioned withinthe interior of the barrel section 120, and/or the plurality of roboticdrilling units 208 may be mounted inside or outside of the barrelsection 120.

FIG. 6 is a perspective illustration of the plurality of roboticdrilling units 208 positioned on the system base 202 and mounted withinrelatively close proximity to one another such that the barrel section120 circumscribes the plurality of robotic drilling units 208 when thebarrel section 120 is mounted to the system base 202. Although four (4)robotic drilling units 208 are shown, any number may be provided. In anembodiment, the robotic drilling units 208 may be mounted in an array.For example, each one of the robotic drilling units 208 may include adrilling unit base 212 (FIG. 7). The drilling unit bases 212 (FIG. 7)may be mounted to the system base 202 in a circular array 206 (FIG. 8)such that when the barrel section 120 is mounted to the system base 202,each one of the drilling unit bases 212 (FIG. 7) is positioned atsubstantially the same distance from the inner face sheet 134 of thebarrel section 120.

FIG. 7 is a side view of an embodiment of the drilling system 200. Thebarrel section 120, shown in phantom lines, may be supported on onefixture 204 or multiple fixtures 204. The fixtures 204 may comprisespacers sized and configured to position the barrel section 120 at avertical location that is complementary to the movement capability ofthe drill end effectors 234 of the robotic drilling units 208. In thisregard, the fixtures 204 may be configured such that the drill endeffectors 234 may form perforations 136 (FIG. 9) in the inner face sheet134 of the barrel section 120 at any vertical location between theforward edge 124 of the barrel section 120 and the aft edge 126 of thebarrel section 120. The fixtures 204 may be comprised of a rigidmaterial and may be configured as simple blocks (not shown) formed ofmetallic or polymeric material and which may be fixedly coupled to thesystem base 202. The fixtures 204 may extend vertically along anyportion of the height of the barrel section and horizontally along anyportion of the circumference of the barrel section 120.

FIG. 8 is a top view of the drilling system 200 illustrating anarrangement of the robotic drilling units 208. Each one of the roboticdrilling units 208 may include a robotic arm assembly 210 having a drillend effector 234 mounted on an end of the robotic arm assembly 210. Therobotic drilling units 208 may be mounted such that drilling unit bases212 are positioned adjacent to a center of the array of the roboticdrilling units 208. In an embodiment, the drilling system 200 maycomprise a single robotic drilling unit 208 or a plurality of roboticdrilling units 208. For example, the drilling system 200 may include two(2) or more robotic drilling units 208 having drilling unit bases 212which may be arranged at a predetermined spacing relative to oneanother, such as a substantially equiangular spacing relative to oneanother.

Referring still to FIG. 8, the plurality of robotic drilling units 208may be configured (e.g., programmed) to drill perforations 136 (FIG. 9)within substantially equivalent arc segments 142 of the barrel section120. For example, for the embodiment shown, the plurality of roboticdrilling units 208 may comprise four (4) robotic drilling units 208. Thedrilling unit bases 212 may be arranged such that the drilling unitbases 212 are positioned at an angular spacing of approximately ninetydegrees relative to one another. In an embodiment, each one of therobotic drilling units 208 may be configured to drill perforations 136(FIG. 9) within an approximate ninety-degree arc segment 142 of thebarrel section 120. However, the robotic drilling units 208 may bepositioned at any location relative to one another and may be configuredto form perforations 136 (FIG. 9) at any circumstantial location or anyvertical location of the barrel section 120.

In FIG. 8, the drill end effector 234 of each one of the roboticdrilling units 208 may be oriented generally radially outwardly awayfrom the drilling unit base 212. The drilling unit bases 212 may bepositioned to provide space for movement of the robotic arm assemblies210 during operation of the drilling system 200. In this regard, therobotic drilling units 208 are simultaneously operable in synchronizedmovement with one another in a manner allowing the drill end effectors234 to simultaneously drill a plurality of perforations 136 (FIG. 9) inthe barrel section 120. The robotic drilling units 208 may be programmedto avoid collisions with one another and with the barrel section 120during the synchronized movement with one another.

FIG. 9 is a side view of one of the robotic drilling units 208 showingthe barrel section 120 supported on fixtures 204 and illustrating adrill bit 236 of one of the drill end effectors 234 forming perforations136 in a predetermined hole pattern 140 along the inner face sheet 134of the inner barrel section 120. In this regard, in an embodiment, eachone of the robotic drilling units 208 may be indexed to the system base202. The barrel section 120 may also be indexed to the system base 202such as with fixtures 204 to provide a means for the drill end effector234 to form perforations 136 within a relatively small positionaltolerance relative to a circumferential direction (not shown) of thebarrel section 120 and relative to an axial direction (not shown) of thebarrel section 120. However, the barrel section 120 and the roboticdrilling units 208 may be indexed relative to one another by othermeans, and are not necessarily limited to being indexed to the systembase 202.

In FIG. 9, the robotic drilling units 208 may be operated in a manner todrill the perforations 136 in the inner face sheet 134 such that apercent-open-area 144 in one section 148 of the inner face sheet 134 isdifferent than the percent-open-area 144 in another section 150 of theinner face sheet 134. In this regard, the robotic drilling units 208 maybe programmed to drill perforations 136 to provide a greaterpercent-open-area 144 in a first section 148 of the inner face sheet 134relative to drilling perforations 136 to provide a lowerpercent-open-area 144 in a second section 150 of the inner face sheet134. For example, the second section 150 with a smallerpercent-open-area 144 may be located adjacent to a forward edge 124and/or an aft edge 126 of the barrel section 120, and the first section148 with a larger percent-open-area 144 may be located in an interiorregion (not shown) of the inner barrel section 120 between the forwardedge 124 and the aft edge 126. However, the robotic drilling 208 unitsmay drill the perforations 136 such that the percent-open-area 144 inthe inner face sheet 134 is different at different circumferentialsections (not shown) of the barrel section 120, or the percent-open-area144 of the inner barrel section 120 may vary in a different manner thanthe above-noted embodiments.

In FIG. 9, one or more of the robotic drilling units 208 may have asix-axis robotic arm assembly 210 which may allow for accuratelypositioning the drill end effector 234 at any desired location andorientation along the inner face sheet 134. As the drill end effector234 is positioned and oriented at a desired location of a perforation136, the drill end effector 234 may be moved axially to drive therotating drill bit 236 into the inner face sheet 134 to form aperforation 136. Alternatively, the drill end effector 234 may bepositioned at a desired location of a perforation 136 on the inner facesheet 134, and the drill end effector 234 may axially drive the rotatingdrill bit 236 along a direction of the drill bit axis 238 to drill theperforation 136 in the inner face sheet 134. In an embodiment, thesix-axis robotic arm assembly 210 may include a first arm 220 which maybe attached to the drilling unit base 212 at a shoulder joint 216. Thefirst arm 220 may be attached to a second arm 226 at an elbow joint 222.The second arm 226 may be attached to the drill end effector 234 at awrist joint 230.

In FIG. 9, the drilling unit base 212 may be configured to rotate abouta vertical base axis 214 relative to the system base 202. The first arm220 may be configured to rotate about a shoulder axis 218 of theshoulder joint 216 coupling the first arm 220 to the drilling unit base212. The second arm 226 may be configured to rotate about an elbow axis224 of the elbow joint 222 coupling the second arm 226 to the first arm220. A portion of the second arm 226 may also be configured to swivelabout a second arm axis 228 extending along a direction from the elbowjoint 222 to the wrist joint 230. The drill end effector 234 may beconfigured to rotate about a wrist axis 232 of the wrist joint 230. Inaddition, the drill end effector 234 may be configured to rotate aboutan end effector axis 235 which may be generally parallel to the drillbit axis 238. In an optional embodiment, the end effector may beconfigured to linearly translate the drill bit 236 along a drill bitaxis 238 such as when drilling a perforation 136 in the inner face sheet134.

In FIG. 9, the robotic arm assembly 210 is shown in a six-axisembodiment. However, the robotic arm assembly 210 may be provided inalternative arrangements. For example, the robotic arm assembly 210 maybe provided in a 3-axis embodiment (not shown), a 4-axis embodiment (notshown), or a 5-axis embodiment (not shown). In addition, the robotic armassembly 210 may be provided in an embodiment having more than six (6)axes. Furthermore, the robotic arm assembly 210 may be configured as amotion control system (not shown), a rigid frame (not shown) havinglinear axes along which the end effector is movable, or any other typeof motion control device for controlling a drill end effector 234 fordrilling perforations 136. In addition, each robotic arm assembly 210may include more than one drill end effector 234. Furthermore, eachdrill end effector 234 may have more than one drill bit 236 forsimultaneously forming perforations 136.

FIG. 10 shows a drill end effector 234 forming a perforation 136 in theinner face sheet 134 of a composite sandwich structure 122 of the innerbarrel section 120. Advantageously, the drilling system 200 provides ameans for accurate and rapid placement of the drill end effector 234 fordrilling perforations 136 in a predetermined hole pattern 140 (FIG. 9).For example, in an embodiment, each one of the drill end effectors 234of a robotic drilling unit 208 may be configured to form up to three (3)or more perforations 136 per second, per drill end effector 234. In anembodiment, the drill end effector 234 may be provided with a drill bit236 configured to form acoustic perforations 136 having a hole diameterof approximately 0.010 to 0.10 inch, although larger or smallerperforations 136 are possible based on the drill bit 236 diameter.

In FIG. 10, for forming perforations 136 in a composite inner face sheet134, the drill end effector 234 may be configured to drive the drill bit236 at a feed rate of approximately 20-60 inches per minute, and atrotational speeds of between approximately 20,000 to 40,000 rpm,although larger or smaller feed rates and larger or smaller rotationalspeeds may be selected based on the material being drilled and thecomposition of the drill bit 236. The drill bit 236 feed rate and thedrill bit 236 rotational speed may be controlled to minimize drill bit236 wear, and such that the perforations 136 may meet tight tolerancesfor roundness and other hole parameters. Significantly, each roboticdrilling unit 208 is configured to quickly and accurately form holepatterns 140 (FIG. 9) at a relatively small center-to-center positionaltolerance (i.e., perforation-to-perforation) such as a center-to-centerpositional tolerance of approximately 0.010 inch or less. However, thecenter-to-center positional tolerance may be greater than 0.010 inch,such as up to approximately 0.050 inch or greater.

In FIG. 10, one or more of the drill end effectors 234 may include avacuum attachment 240 for removing debris (not shown) such as dust andchips that may be generated during the drilling of the perforations 136.The vacuum attachment 240 may have a hollow (not shown) or open portion(not shown) that may be positioned around the drill bit 236 and may beplaced adjacent to or in contact with the inner face sheet 134 when thedrill bit 236 contacts the inner face sheet 134 and drills a perforation136. The vacuum attachment 240 may include a vacuum port 242 forconnection to a vacuum source (not shown) using a vacuum hose (notshown) for drawing a vacuum 244 on the vacuum attachment 240 for drawingdebris (not shown) from the area surrounding the perforation 136.

In FIG. 10, in a further embodiment, the drilling system 200 may beprovided with an automated bit changer (not shown) for changing thedrill bits 236 using robotic control. In this manner, worn drill bits236 may be replaced after drilling a predetermined quantity ofperforations 136. For example, an automated bit changer (not shown) mayreplace each drill bit 236 after drilling anywhere from approximately1,000 to 30,000 perforations 136, although the drill bits 236 may bereplaced after drilling a smaller or larger quantity of perforations 136than the above-noted range. Depending upon the size (e.g., diameter andheight) of the inner barrel section 120 and the total quantity ofrobotic drilling units 208 that are used, each drill end effector 234may undergo 1 to 20 or more drill bit changes per barrel section 120.

Referring briefly to FIG. 9, in an embodiment, the drill end effectors234 may be controlled to drill perforations 136 in a hole pattern 140 ofvertical rows (not shown) along a height of the barrel section 120. Inthis regard, each drill end effector 234 may drill a vertical row ofperforations 136, and the drill end effector 234 may be rotated aboutthe vertical base axis 214 to allow the drill end effector 234 to drillanother vertical row of perforations 136 adjacent to thepreviously-drilled vertical row of perforations 136. The drill endeffectors 234 may also be controlled to drill perforations 136 inhorizontal rows (not shown), or in any other direction or combination ofdirections. As indicated above, the robotic arm assemblies 210 may beoperated in a synchronized manner such that the drill end effectors 234are maintained at a generally equiangular spacing from one anotherduring the simultaneous drilling of perforations 136 in the inner facesheet 134 of the barrel section 120. For example, for a drilling system200 having four (4) robotic drilling units 208, the drill end effectors234 may be maintained at an angular separation of approximately ninety(90) degrees from each other during the simultaneous drilling ofperforations 136 in the inner face sheet 134.

FIG. 11 is a cross sectional view of a drill bit 236 of the drill endeffector 234 forming a perforation 136 in the inner face sheet 134 of acomposite sandwich structure 122. In an embodiment, the drill endeffector 234 may include a drill stop (not shown) to control a depth 138at which the drill bit 236 extends into the composite sandwich structure122, and minimize the depth 138 of the drill bit 236 into the core 128material. Furthermore, a drill stop (not shown) may stabilize the drillend effector 234 when drilling the perforation 136 to prevent lateralmovement of the drill bit 236 relative to the perforation 136, and whichmay advantageously avoid a non-conformance regarding the positionaltolerance, roundness tolerance, or other tolerance parameters of theperforation 136. In an embodiment, each drill end effector 234 mayinclude a non-contact method of gauging the depth 138 at which eachperforation 136 is drilled such as by using a laser device (not shown),an ultrasonic device (not shown), and other non-contact device. Thedepth 138 of drilling may also be controlled by a controller (not shown)controlling the drill end effector 234.

FIG. 12 is a block diagram of an embodiment of a drilling system 200.The drilling system 200 may include a plurality of robotic drillingunits 208. Each one of the robotic drilling units 208 may include arobotic arm assembly 210 as described above. A drill end effector 234may be coupled to the end of each one of the robotic arm assemblies 210of each robotic drilling unit 208. The robotic drilling units 208 may besimultaneously operable in synchronized movement with one another suchthat the drill end effectors 234 may simultaneously drill a plurality ofperforations 136 in the barrel section 120.

In FIG. 12, the barrel section 120 may comprise an inner barrel section120 of an engine inlet 114 such as of a gas turbine engine 108 (FIG. 3),as indicated above. In an embodiment, the barrel section 120 may beformed as a composite sandwich structure 122. The composite sandwichstructure 122 may have an outer face sheet 132, a core 128, and an innerface sheet 134 which may be assembled or bonded together to form aone-piece engine inlet inner barrel section 120. The drilling system 200may rapidly and accurately form a plurality of perforations 136 in apredetermined hole pattern of perforations 136 (FIG. 9) in the innerface sheet 134 to provide a predetermined percent-open-area 144 for theinner barrel section 120 to meet acoustic performance requirements.

FIG. 13 is an illustration of a flow chart including one or moreoperations that may be included in a method 300 of fabricating an engineinlet 114 (FIG. 3). Step 302 of the method may include providing abarrel section 120 (FIG. 3) such as an inner barrel section 120 (FIG. 3)of an engine inlet 114 (FIG. 3). As indicated above, the inner barrelsection 120 (FIG. 3) may be provided as a one-piece composite sandwichstructure 122 (FIG. 3). In such a composite sandwich structure 122 (FIG.3), the inner face sheet 134 (FIG. 3) may be formed of compositematerial and the outer face sheet 132 (FIG. 3) may be formed ofcomposite material (e.g., fiber-reinforced polymeric matrix material).However, the inner face sheet 134 (FIG. 3) and/or the outer face sheet132 (FIG. 3) may be formed of metallic material, or a combination ofmetallic material and non-metallic material.

As indicated above, the core 128 (FIG. 3) may comprise honeycomb coreformed of metallic material and/or non-metallic material and may includealuminum, titanium, aramid, fiberglass, or other core materials. Theengine inlet 114 (FIG. 3) inner barrel section 120 (FIG. 3) may befabricated as a one-piece composite sandwich structure 122 (FIG. 3)formed in a single-stage cure. As described above, the barrel section120 (FIG. 3) may be provided in a single-stage cure wherein the innerface sheet 134 (FIG. 3), the core 128 (FIG. 3), and the outer face sheet132 (FIG. 3) may be laid up on a layup mandrel, after which heat and/orpressure may be applied to the layup (not shown) for a predeterminedtime for curing in a single stage.

Step 304 of the method 300 of FIG. 13 may include mounting and indexingthe inner barrel section 120 (FIG. 7) to a system base 202 (FIG. 7). Inthis regard, the inner barrel section 120 (FIG. 7) may be supported on aplurality of fixtures 204 (FIG. 7) which may be mounted to the systembase 202 (FIG. 7). The fixtures 204 (FIG. 7) may fixedly position theinner barrel section 120 (FIG. 7) on the system base 202 (FIG. 7) whichmay comprise a table (not shown), an assembly (not shown), or otherrelatively rigid structure configured to support the inner barrelsection 120 (FIG. 7) and prevent movement thereof during the drilling ofthe perforations 136 (FIG. 9) in the inner barrel section 120 (FIG. 7).

As indicated above, the fixtures 204 may be positioned at spacedintervals around a perimeter (not shown) of the inner barrel section 120such as along the aft edge 126 (FIG. 9) or forward edge 124 (FIG. 9) ofthe inner barrel section 120. The fixtures 204 may include mechanicalindexing features (not shown) to index the inner barrel section 120 tothe fixtures 204. A laser system (not shown) may be implemented to aidin positioning the inner barrel section 120 relative to the fixtures204. The inner barrel section 120 may be mechanically coupled to thefixtures 204 to rigidly clamp the inner barrel section 120 in position.

Step 306 of the method 300 of FIG. 13 may include indexing the pluralityof robotic drilling units to the system base 202 (FIG. 7) as shown inFIG. 7. In an embodiment, each one of the plurality of robotic drillingunits 208 (FIG. 7) may have a drilling unit base 212 (FIG. 7) that maybe directly mounted to the system base 202 and indexed to the systembase 202 and/or to the fixtures 204 (FIG. 7) supporting the inner barrelsection 120 (FIG. 7). For example, the drilling unit bases 212 of therobotic drilling units 208 may be mounted to the system base 202 and maybe located inside the inner barrel section 120 as shown in FIG. 7.Alternatively, the drilling unit bases 212 may be located outside of theinner barrel section 120 and the drill end effectors 234 (FIG. 7) of therobotic arm assemblies 210 (FIG. 7) may extend inside the inner barrelsection 120 to drill the perforations 136 (FIG. 9). In a furtherembodiment, the robotic drilling units 208 may be supported by astructure (not shown) that is located separate from the system base 202and separate from the barrel section 120. For example, the drilling unitbases 212 of the robotic drilling units 208 may be mounted to anoverhead fixture (not shown) that may be indexed to the system base 202and/or to the fixtures 204 supporting the inner barrel section 120. Thedrill end effectors 234 may extend inside the barrel section 120 todrill the perforations 136.

Step 308 of the method 300 of FIG. 13 may include acoustically treatingthe engine inlet 114 (FIG. 9) by robotically drilling a plurality ofperforations 136 (FIG. 9) into the inner face sheet 134 (FIG. 9) of thecomposite sandwich structure 122 (FIG. 9) engine inlet 114 inner barrelsection 120 (FIG. 9) such as after final cure of the composite sandwichstructure 122. For example, the method 300 may include roboticallydrilling the plurality of perforations 136 in the inner barrel section120 using a plurality of the robotic drilling units 208 (FIG. 9). Themethod 300 may include simultaneously drilling the plurality ofperforations 136 in the inner face sheet 134 using the drill endeffectors 234 (FIG. 9) to provide a predetermined percent-open-area 144of the inner face sheet 134. In an embodiment, each one of the roboticdrilling units 208 may include a robotic arm assembly 210 (FIG. 9)configured as a three-axis, four-axis, five-axis, or six-axis armassembly respectively having three axes, four axe, five axes, and sixaxes. The robotic arm assemblies 210 may be programmed to move the drillend effectors 234 in a synchronized manner relative to one another todrill the perforations 136 at a relatively rapid rate. For example, eachone of the drill end effectors 234 may be configured to form 2-3 or moreperforations 136 per second.

The method 300 (FIG. 13) may include drilling the perforations 136 (FIG.9) in a predetermined hole pattern 140 (FIG. 9) in the engine inlet 114(FIG. 9) inner barrel section 120 (FIG. 9) which may have a honeycombcore 128 (FIG. 11). The robotic drilling units 208 (FIG. 9) may beconfigured to control the drill end effectors 234 (FIG. 9) to drill theperforations 136 normal (e.g., perpendicular) to the inner face sheet134 (FIG. 10). In addition, the robotic drilling units 208 may beconfigured to drill the perforations 136 at a spaced distance to thecell walls 131 (FIG. 11) of the honeycomb core 128. In this regard, therobotic drilling units 208 may be configured to drill one or moreperforations 136 in each of the cells 130 at a distance from the cellwalls 131 to avoid drilling into the cell walls 131. The roboticdrilling units 208 may drill the perforations 136 in a hole pattern 140that may be configured complementary to the geometry and size of thecells 130 of honeycomb core 128. For example, the hole pattern 140 (FIG.9) may be such that one perforation 136 (FIG. 11) is drilled into eachcell 130 (FIG. 11) such as at an approximate center (not shown) of eachcell 130. However, the hole pattern 140 may be such that two or moreperforations 136 may be drilled into each cell 130 of the honeycomb core128 (FIG. 11).

The robotic drilling units 208 (FIG. 9) may be configured to index orposition the hole pattern 140 (FIG. 9) relative to the cell 130 (FIG.11) centers (not shown) or relative to the cell walls 131 (FIG. 11) of ahoneycomb core 128. For example, for a honeycomb core 128 having agenerally uniform arrangement of cells 130 of equal size and shape, therobotic drilling units 208 may be configured to establish a location ofone of the cell walls 131 in order to index a hole pattern 140 relativeto the locations of the cell 130 of the honeycomb core 128. Afterestablishing the location of one or more cell walls 131, the roboticdrilling units 208 may be configured to drill the hole pattern 140 ofperforations 136 in the inner face sheet 134 of the honeycomb core 128such that each perforation 136 is drilled at a predetermined location ineach cell 130 such as at a center (not shown) of each cell 130, or at apredetermined location or spaced distance 146 relative to the cell walls131 of each cell 130. The hole pattern 140 may also be such thatmultiple perforations 136 may be drilled into each cell 130 and may belocated at predetermined distances or spaced distances 146 from the cellwalls 131 of each cell 130.

Advantageously, the robotic drilling units 208 (FIG. 9) may beconfigured to form perforations 136 (FIG. 9) within a relatively highpositional tolerance (e.g., 0.010 inch on centers) in the hole-to-holespacing. In addition, as indicated above, each one of the drill endeffectors 234 (FIG. 10) may include a vacuum attachment 240 (FIG. 10)configured to be positioned adjacent to or against the inner face sheet134 during the drilling of the perforations 136. The vacuum attachment240 may include a vacuum port 242 (FIG. 11) that may be coupled to avacuum source (not shown) via a vacuum hose (not shown) to provide avacuum 244 (FIG. 10) for suctioning dust, chips, and other debris awayfrom a location where a perforation 136 is being drilled.

Step 310 of the method 300 of FIG. 13 may include periodically changingthe drill bits 236 (FIG. 10) of the drill end effectors 234 (FIG. 10)during the process of drilling perforations 136 (FIG. 10) in the innerbarrel section 120 (FIG. 10). In an embodiment, the method may includerobotically changing the drill bits 236 using an automated bit changer(not shown). Drill bits 236 may be replaced after drilling apredetermined quantity of perforations 136. For example, each drill bit236 may be replaced after drilling several thousand or more perforations136. The frequency at which the drill bits 236 may be replaced may beaffected by the thickness of the inner face sheet 134 (FIG. 11), thematerial composition of the inner face sheet 134, the rotational speedof the drill bit 236, the feed rate of the drill bit 236, the materialcomposition of the drill bit 236, and other factors. In an embodimentnot shown, the method may include detecting when a drill bit 236 isbecoming dull, at which point the method may include replacing the dulldrill bit 236 with a new or sharpened drill bit (not shown).

Advantageously, the drilling system 200 (FIG. 12) and method disclosedherein provides for operating a plurality of robotic drilling units 208(FIG. 12) in a synchronized manner to accurately and rapidly formperforations 136 (FIG. 12) in the inner face sheet 134 (FIG. 12) of aninner barrel section 120 (FIG. 12) with a high degree of repeatability.In addition, the drilling system 200 provides a means for formingperforations 136 with a significant reduction in defects and reworkcommonly associated with conventional methods. In this regard, thedrilling system 200 and method disclosed herein may avoid theabove-mentioned defects of missing perforations (not shown) and/orblocked perforations (not shown) during subsequent processing in amulti-stage barrel section fabrication process (not shown), and theassociated reduction in percent-open-area 144 (FIG. 9) in the inner facesheet 134 of the inner barrel section 120.

As indicated above, the percent-open-area 144 (FIG. 9) of the inner facesheet 134 is the total area of the perforations 136 (FIG. 9) as apercentage of the surface area (not shown) of the inner face sheet 134(FIG. 9) and is a characteristic for measuring the overall effectivenessor acoustic-attenuating capability of the inner barrel section 120 (FIG.9). In FIG. 9, the robotic drilling units 208 (FIG. 9) may be operatedin a manner to drill perforations 136 to provide a percent-open-area 144(FIG. 9) in one section 148 (FIG. 9) of the inner face sheet 134 that isdifferent than the percent-open-area 144 in another section 150 (FIG. 9)of the face sheet 134. For example, in FIG. 9, a first section 148 ofperforations 136 drilled in the inner face sheet 134 may have a largerpercent-open-area 144 relative to a second section 150 of perforations136 which may be located adjacent to a forward edge 124 and/or an aftedge 126 of the barrel section 120. However, as indicated above,differing sections (not shown) of percent-open-area 144 may be arrangedin any manner along the inner face sheet 134 of the inner barrel section120 (FIG. 9), and are not limited to the arrangement shown in FIG. 9 ordescribed above.

Referring to FIGS. 14-15, embodiments of the disclosure may be describedin the context of an aircraft manufacturing and service method 400 asshown in FIG. 14 and an aircraft 402 as shown in FIG. 15. Duringpre-production, exemplary method 400 may include specification anddesign 404 of the aircraft 402 and material procurement 406. Duringproduction, component and subassembly manufacturing 408 and systemintegration 410 of the aircraft 402 takes place. Thereafter, theaircraft 402 may go through certification and delivery 412 in order tobe placed in service 414. While in service by a customer, the aircraft402 is scheduled for routine maintenance and service 416 (which may alsoinclude modification, reconfiguration, refurbishment, and so on).

Each of the processes of method 400 may be performed or carried out by asystem integrator, a third party, and/or an operator (e.g., a customer).For the purposes of this description, a system integrator may includewithout limitation any number of aircraft manufacturers and major-systemsubcontractors; a third party may include without limitation any numberof venders, subcontractors, and suppliers; and an operator may be anairline, leasing company, military entity, service organization, and soon.

As shown in FIG. 15, the aircraft 402 produced by exemplary method 400may include an airframe 418 with a plurality of systems 420 and aninterior 422. Examples of high-level systems 420 include one or more ofa propulsion system 424, an electrical system 426, a hydraulic system428, and an environmental system 430. Any number of other systems may beincluded. Although an aerospace example is shown, the principles of theinvention may be applied to other industries, such as the automotiveindustry.

Apparatus and methods embodied herein may be employed during any one ormore of the stages of the production and service method 400. Forexample, components or subassemblies corresponding to production process408 may be fabricated or manufactured in a manner similar to componentsor subassemblies produced while the aircraft 402 is in service. Also,one or more apparatus embodiments, method embodiments, or a combinationthereof may be utilized during the production stages 408 and 410, forexample, by substantially expediting assembly of or reducing the cost ofan aircraft 402. Similarly, one or more of apparatus embodiments, methodembodiments, or a combination thereof may be utilized while the aircraft402 is in service, for example and without limitation, to maintenanceand service 416.

Many modifications and other embodiments of the disclosure will come tomind to one skilled in the art to which this disclosure pertains havingthe benefit of the teachings presented in the foregoing descriptions andthe associated drawings. The embodiments described herein are meant tobe illustrative and are not intended to be limiting or exhaustive.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

What is claimed is:
 1. A method of fabricating an engine inlet,comprising the steps of: providing an engine inlet inner barrel sectionconfigured as a composite sandwich structure having an inner face sheet;robotically drilling, using a plurality of synchronized robotic drillingunits, a plurality of perforations in the inner face sheet after finalcure of the composite sandwich structure, wherein the drilling comprisesindexing a hole pattern of the perforations to one or more cell walls ofa honeycomb core of the composite sandwich structure, and positioningthe hole pattern such that each perforation is located at a spaceddistance from the cell walls; and forming the plurality of perforationsin a quantity providing a predetermined percent-open-area of the innerface sheet.
 2. The method of claim 1, wherein the step of providing theengine inlet inner barrel section comprises: providing the engine inletinner barrel section as a one-piece composite sandwich structure curedin a single stage.
 3. The method of claim 1, wherein the step ofrobotically drilling the plurality of perforations comprises: drillingthe perforations to provide a percent-open-area in one section of theinner face sheet that is different than the percent-open-area in anothersection of the inner face sheet.
 4. The method of claim 1, wherein thestep of robotically drilling the plurality of perforations comprises:drilling the plurality of perforations using a plurality of roboticdrilling units positioned inside the barrel section.
 5. The method ofclaim 4, wherein the step of robotically drilling the plurality ofperforations using the plurality of robotic drilling units comprises:operating the robotic drilling units in synchronized movement with oneanother inside the engine inlet inner barrel section.
 6. The method ofclaim 5, wherein the step of operating the robotic drilling units insynchronized movement with one another comprises: simultaneouslydrilling the plurality of perforations in the inner face sheet usingdrill end effectors of the plurality of robotic drilling units.
 7. Themethod of claim 1, further comprising: positioning a drilling unit baseof each robotic drilling unit inside the engine inlet inner barrelsection.
 8. The method of claim 1, further comprising: indexing theengine inlet inner barrel section and the robotic drilling units to atleast one fixture supporting the barrel section.
 9. A method offabricating an engine inlet, comprising the steps of: providing anengine inlet inner barrel section as a one-piece composite sandwichstructure cured in a single stage and having an inner face sheet and ahoneycomb core; drilling, using a plurality of robotic drilling units, aplurality of perforations in the inner face sheet after final cure ofthe composite sandwich structure, wherein the drilling comprisesindexing a hole pattern of the perforations to one or more cell walls ofa honeycomb core of the composite sandwich structure, and positioningthe hole pattern such that each perforation is located at a spaceddistance from the cell walls; operating the plurality of roboticdrilling units in synchronized movement with one another tosimultaneously drill the plurality of perforations; and forming theplurality of perforations in a quantity providing a predeterminedpercent-open-area of the inner face sheet.